Lipoproteins function to transport lipids around the body. Lipids are generally hydrophobic, while the extracellular environment is generally aqueous. Apolipoproteins bind to lipids, such as cholesterol and triglycerides, and facilitate their transport through the aqueous environment. Apolipoprotein B (apoB) represents most of the protein content in low density lipoprotein (LDL), and is also present in intermediate-density lipoproteins (IDL) and very low density lipoproteins (VLDL). Apolipoprotein AI (apoAI) is the principal protein in high density lipoprotein (HDL) and represents about 70%.
The total cholesterol/HDL cholesterol ratio and the LDL/HDL cholesterol ratio are two indicators of vascular disease risk, including cardiovascular disease (CVD) risk. For example, an increase in the total cholesterol concentration, and specifically LDL cholesterol, is an atherogenic lipid marker. Reduced HDL cholesterol concentration is associated with various risk factors, including components of the metabolic syndrome.